The invention relates generally to the field of on-line testing of moisture content of processed material. In particular, the invention relates to an on-line moisture analyzer for testing the moisture content of ore concentrates.
The moisture content of material being processed can be an important factor in assuring the quality of final product and in controlling manufacturing parameters to obtain an optimal moisture content. For example, in the iron ore industry raw ore is ground and mixed with water to form a slurry that is processed to remove undesired constituents such as sand. After processing, the slurry is filtered to remove the bulk of the moisture and the resulting xe2x80x9cfilter cakexe2x80x9d is rolled in a drum to form pellets. The filtering process is controlled to produce a filter cake having a desired moisture content and the rolling process is optimized based on filter cake moisture content. The rolling process requires a relatively constant moisture content in the filter cake for proper processing. Deviations from the desired content can compromise the quality of the pellets. Therefore, it is critical to have real time information about the moisture content of the filter cake to achieve consistent high quality pellets.
Numerous techniques have been developed to test the moisture content of filter cakes and other ore concentrates. A reliable and relatively simple way to determine moisture content is to take a sample, weigh the sample, bake the sample or otherwise remove the moisture from the sample, and then weigh the sample again. The difference in the weight of the sample before and after baking corresponds to the amount of moisture that was present in the sample. This weighing technique is typically done manually in a laboratory environment due to the relatively involved process of obtaining, weighing, and baking the sample. Taking the sample to a separate location increases the delay between the taking of the sample and the availability of useful moisture information to process controls. In addition, the introduction of technicians into the measurement process means that human error may affect the accuracy of the results and that measurements can only be taken when a technician is on duty.
Existing on-line testing techniques monitor filter cake characteristics that are related to moisture content. These characteristics include electrical conductivity, dielectric properties, microwave absorption, and radio frequency transmission. Because the characteristics are affected by properties other than moisture content, such as the precise mineral content of the ore or ph of the water, they are unreliable and may only be accurate to about +/xe2x88x920.50% (industry standard is +/xe2x88x920.10%). Infra-red reflectance has been used as an indication of moisture content, but this method has proven unsatisfactory in a factory setting because it is susceptible to errors caused by water vapor or reflective surfaces in the optical path. Neutron activation principles have been employed that determine the hydrogen content of the concentrate from which moisture content is inferred. The devices used in this technique are bulky, complex, and require extensive shielding to diffuse the emitted radiation. One other technique involves correlating moisture content to the drag forces exerted on a probe by the concentrate moving on a conveyor. This method depends on a uniform distribution of concentrate on the conveyor, which is not realistic in a manufacturing environment.
According to the present invention, an apparatus is provided for measuring the moisture content of a concentrate, such as an iron ore concentrate. According to an embodiment of the invention, a sample container receives and holds a sample of the concentrate. A conveyance member has a plurality of conveyance devices that are connected to the sample container that each move the sample container about a single axis. A scale is accessible by the conveyance member for weighing the sample. An oven having an oven door accessible by the conveyance member heats the sample to remove the moisture. A controller controls the conveyance member and the oven and a processing unit receives data from the scale to determine a moisture content based on the data.
In an embodiment, the conveyance member is a sliding carriage, such as a horizontal linear slide, having a rotatable arm for rotating the sample container about an axis of rotation. A pair of opposing fingers apply a gripping force to the sample container and may have at least one pin insertable into the sample container. A pneumatic vertical lift lifts the arm and the arm features a torque limiting brake.
In an exemplary embodiment, the oven door has a complimentary shape relative to a cross section of the sample container and conveyance member and is adapted to open in response to a signal from the controller. The processing unit determines the moisture content of the sample by finding a difference between a first weight of the sample container before the controller causes the conveyance device to move the sample container into the oven and a second weight of the sample container after the controller causes the conveyance device to remove the sample container from the oven. A plow mechanism in communication with the sample container may be provided for distributing the sample in the sample container. According to a feature of the invention a sweeping mechanism removes sample residue from the sample container after the analysis is complete.